In the prior art, due to the inconsistency between the equipment voltage ground (EVG) in the lamp circuit apparatus and the actual grounding, there might be dangerous voltage on the lamp or there might be phenomena of damage to the lamp circuit.
In the case of detecting the end of lamp life, it is very advantageous to directly connect a terminal of the lamp to the equipment voltage ground (EVG), because in this way, the voltage on the lamp to be detected will no longer contain a half value of the DC component of the rectified voltage of the rectification circuit. However, on the other hand, such kind of circuit has a big problem, because when the internal equipment voltage ground (EVG) contacts the external ground terminal, the lamp might be ignited, and this may be one of the following case, i.e., only one terminal of the lamp is connected (e.g., during maintenance) while another terminal thereof is contacted by a person, as shown in FIG. 1. In the known lamp circuit apparatus as shown in FIG. 1, the circuit forms a closed loop via the voltage source, external ground, human body, lamp, internal ground EVG, diode D4 and filtering circuit C1, C6.
In addition, when the lead of the EVG towards the lamp contacts the external ground, there might be the danger of damaging the lamp circuit apparatus despite if the lamp is connected to the lamp circuit apparatus or not, as shown in FIG. 2.
For the above reasons, such lamp circuit apparatus in the European market has the above-mentioned danger hiding behind, while in the U.S., such lamp circuit apparatus is not employed due to the high mains voltage.